International standard ISO/IEC 11801 specifies general-purpose telecommunication cabling systems (structured cabling) that are suitable for a wide range of applications (analog and ISDN telephony, various data communication standards, building control systems, factory automation). The ISO/IEC standard covers both balanced copper cabling and optical cabling.
The standard defines several classes, or categories, of twisted-pair copper interconnects, which differ in the maximum frequency for which a certain channel performance is required. For example, category 5e utilizes frequencies up to 100 MHz, while category 6 utilizes frequencies up to 250 MHz. Category 6a utilizes frequencies up to 500 MHz, and category 7 uses frequencies of up to 1 GHz.
Telecommunication cabling systems, when implemented using electrical signals, utilize twisted pair wiring and electrical connectors to form communication channels between computing systems, routers, or other telecommunications and networking equipment. The wiring, formed as cables, as well as the electrical connectors, is required to meet electrical performance criteria set by such ISO standards. When telecommunications equipment, including telecommunications connectors, is manufactured, such equipment is typically tested to ensure compliance with electrical performance characteristics.
Existing systems that are used to test the electrical performance of twisted pair connectors or other networking devices typically use a test station that transmits electrical signals to the design under test, and measures the resulting electrical performance of that design. Such systems generally include a balun, which is a type of electrical transformer that converts differential electrical signals to single-ended (e.g., grounded) electrical signals, and vice versa. Such baluns are used in test fixtures to translate test signals to differential signals for transmission through the networking equipment to test its performance.
As signal frequencies increase, use of baluns increasingly becomes problematic. This is because the baluns included in such circuitry introduce some signal degradation (e.g., crosstalk and common-mode effects) leading to signal loss. Although this is not a substantial effect at lower frequencies and within more generous signal loss thresholds available in category 5, 5e, 6, or even 6a frequencies, when signal frequencies are at 1 GHz or higher, the signal degradation attributable to the balun represents a greater proportion of the overall loss in the test circuit. This is both because of the increased signal degradation attributed to the balun at high frequencies, as well as the increased performance requirements of such high frequency standards. In either case, use of baluns to convert between single-ended and differential signals can obscure the actual performance characteristics of the networking equipment design under test.
For these and other reasons, improvements are desirable.